The present invention relates to an electron microscope and positioning method and more particularly to an electron microscope having an improved mechanical stage mover for moving a visual field of the specimen and an electrical shifter for deflecting an electron beam transmitted from a specimen on the stage. The mover and shifter are selectively controlled from a control panel so as to move in minute or fine increments the visual field of the specimen keep the constant direction of the image in accordance with the method of the present invention.
In a conventional electron microscope, the mechanical stage mover and the electrical shifter for deflecting the electron beam transmitted from the specimen are selectively exchanged by manually controlling a common control knob according to a magnification without changing the constant moving direction of an image.
The mechanical stage mover has motors which respectively and linearly move the stage to intersecting X and Y directions and the maximum moving range of the mechanical stage moving means is usually .+-.1 mm and the minimum moving range is about 100 .ANG. which is determined by the accuracy of the motor or gear used in the mechanical stage mover.
The conventional electrical shifter is installed under an objective lens and deflects the electron beam transmitted from the specimen on the stage so as to shift in minute or fine increments the visual field of the specimen. The maximum moving range of the electrical shifter is usually .+-.1 .mu.m in order to avoid undesired aberration influences in the electro-optical system. It is also possible to make the minimum moving range smaller than about 1 .ANG. by improving the stability of the current flowing in the deflecting coil.
When observing the specimen with a low magnification, the conventional mechanical stage mover is used, and when observing with a high magnification, the electrical shifter is used. In a middle magnification situation between the low magnification however, and the high magnification, the operator must frequently select the mechanical mover or the electrical shifter. The U.S. Pat. No. 4,494,000, and Japanese Patent Laid-open documents 55-90042 and 59-16256 are cited as examples of such a device.
Further, U.S. Pat. No. 4,520,264 disclose an image forming lens system which can rotate the final image without the necessity of an additional lens or lenses.
Nevertheless, the moving direction of the image of the specimen in the conventional electron microscope changes more than just a little when the magnification of the electron microscope is changed. Because the magnetic fields of the objective lens, the electrical shifter and a magnification lens under the electrical shifter affect the rotation of the electron beam, it is difficult to correct not to rotate the image of the specimen.